In the prior art, such as illustrated in German Utility Model Registration No. 74.08.66l, separate angle-iron pieces are used in connection with supporting flanges which are attached to respective metal duct walls or segments arranged substantially perpendicular to each other. The supporting flanges are secured to the respective duct walls, as for example by spot welding; and the assembly of the duct walls and supporting flanges are usually shipped in disassembled form to the construction site and when delivered, are assembled at the site. The angle irons (or other angle pieces) are then inserted within the supporting flanges and secured to the base or other supporting structure.
This prior art arrangement, while generally satisfactory, nevertheless has a number of inherent disadvantages. With the first angle piece already inserted, it is difficult to insert the second piece; the second piece is often lifted up by the first piece and gets stuck in the profile of the respective supporting flange. Thus, the second piece must be hammered into its final position, which widens the profile space as the second piece is forced upwardly by the first piece. the second piece, after insertion, rests loosely in its respective supporting flange, whose profile is stretched during the insertion of the second piece therein. A second disadvantage is encountered in that the two angle pieces experience a strong bending stress between the respective legs and contact areas thereof; and as a result, the angle pieces bend easily in the area between the leg and contact areas. The stability or resistance to bending is limited, which is a disadvantage when two adjacent duct segments are being sealed.
Since insertion of the second angle piece, once the first piece is inserted, is difficult, only relatively-thin guages of sheet metal can be used for the respective angle pieces. Therefore, the bending stability cannot be readiy improved by using thicker guages of material. The angle pieces have a relative loose contact, especially since the second piece is disposed loosely due to the stretched profile of the supporting flange, and thus the two angle pieces may be displaced from their secured position when encountering even a relatively minimal stress.
These loose pieces may slip out during transport and assembly, which is a further disadvantage. In an attempt to correct this problem, the second piece has been held in place by a rivet carried by a hole in the second piece and received through the profile of the respective supporting flange. The pressing through of these rivets is performed by a special pneumatic tool, which necessitates a further operation.